The overall goals of the proposed research are: 1) to examine the effects of physical exercise on the activity of the enzyme lipoprotein lipase in the heart, skeletal muscle and adipose tissue of rats and 2) to investigate, in vitro, the factors which participate in the regulation of lipoprotein lipase activity in the rat myocardium. Published data indicate that physical exercise lowers the concentration of plasma triglycerides. They also indicate that this effect may be due, at least in part, to increased rates of triglyceride fatty acid removal from the circulation. Lipoprotein lipase is the enzyme responsible for the uptake of plasma triglyceride fatty acids by extra-hepatic tissues. Preliminary data from our laboratory indicate that the lipoprotein lipase activity in the heart and skeletal muscle of exercised rats is significantly higher than that of unexercised animals. We plan to submit rats, under different physiological conditions, to programs of regular and acute physical exercise. We will attempt to correlate changes in the plasma triglyceride concentration with changes in lipoprotein lipase activity in the tissues. The concentration of serum insulin and growth hormone in animals submitted to physical exercise will be measured by radioimmunoassay. The factors which regulate lipoprotein lipase activity in tissues other than adipose tissue are not known. We plan to study the regulation of myocardial enzyme activity in vitro, using the isolated perfused rat heart. With this system, which can be maintained metabolically active for long periods, we intend to examine the effects which serum from fed and starved rats have on the enzyme activity. We will also study the effects of heparin, glucose, insulin, amino acids and cyclohexamide in this system.